Bounce-suppressing arrangement for separable electrical contacts



Sept. 15, 197 R. P. LUPISH ETAL 3,529,111

BOUNCE-SUPPRESSING ARRANGEMENT FOR SEPARABLE ELECTRICAL CONTACTS Filed Feb. 28. 1968 2 Sheets-Sheet 1 FIG. 7.

WITH WEIGHT CONTACT CLOSED CONTACT- OPEN INVENTORS Ronald P. Luplsh 0nd Stanislaw A. Milionowicz NO WEIGHT CONTACT CLOSED CONTACT OPEN Sept. 15, R, sg-q ETAL 3,529,111

BOUNCE-SUPPRESSING ARRANGEMENT FOR SEPARABLE ELECTRICAL CONTACTS Filed Feb. 28. 1968 2 Sheets-Sheet FIG.2.

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CLOSING CLOSED OPEN FIGS.

United States US. Cl. 200-166 11 Claims ABSTRACT OF THE DISCLOSURE A circuit interrupter having separable contacts, susceptible to bouncing conditions, has associated with the stationary contact an inertia member, or weight, which is supported in a loose condition relevant to the stationary contact. During the closing operation, the impact of closing of the movable contact against the stationary contact causes a compression wave to pass through the stationary contact and be absorbed by the inertia member, which member moves in the closing direction to absorb part of the kinetic energy of the movable contact. Subsequently, the inertia member, or inertia weight settles to its original state, either moving freely or enclosed within a dashpot device to gradually absorb the returning energy.

BACKGROUND OF THE INVENTION When the movable contact of an electrical circuit interrupter strikes its mating stationary contact at the end of a high-velocity contact-closing stroke, there is a tendency for the contacts to bounce, first apart and then together in a repetitive fashion. If the contacts are closed on an energized circuit, there will be an are established between them each time they separate during the bouncing period. As is well known, such arcs can produce objectionable contact erosion and can also produce objectionable contact welding.

Numerous schemes have been proposed to suppress contact bounce, and thus eliminate the above-described erosion and welding problems, but these schemes have generally been subject to serious disadvantages. For example, many of the proposed schemes have not been very effective; many have been quite complicated; and many have necessitated larger and more powerful operating devices for closing the contacts.

The present invention has for its field of application, a circuit interrupter having separable contacts in which, generally, high-velocity forces and high-energy impact closing forces are present during the closing operation of the interrupter. The present invention is particularly concerned with means for dissipation of a portion of the closing energy during the closing operation of a circuit interrupter, so that a bouncing condition will be avoided.

SUMMARY OF THE INVENTION A general object of the present invention is to reduce the bouncing conditions, which are present in a circuit interrupter having separable contacts which close under high-energy and high-velocity conditions.

A more specific object of the present invention is to provide an improved circuit interrupter in which an inertia member, or an inertia weight is associated with the stationary contact structure, such weight or inertia member being free to move at the end of the closing stroke to absorb some of tne impact of the movable contact.

Another object of the present invention is the provision of an improved bounce-suppressing means incorporating a block of metal, which is movable, and has its motion atcnt confined to a dashpot to gradually absorb some of the returned energy of the block of metal or inertia weight.

Still a further object of the present invention is to provide an improved vacuum-type circuit interrupter, which is particularly susceptible to welding conditions, by virtue of the oxygen-free atmosphere within the vacuum envelope, and to associate with the stationary contact of the vacuum interrupter an inertia member, or inertia weight, which will absorb, through the compression wave, some of the impact closing energy of the movable contact of the vacuum-type circuit interrupter. This problem is particularly critical in vacuum-type circuit interrupeters due to the non-oxidizing conditions present within the vacuum envelope. In other words, in a vacuum-type circuit interrupter, due to the oxygen-free atmosphere, conditions for welding between the separable contacts are highly favorable due to the pre-arcing, which occurs during the closing operation, and due to the fact that the contacts may become molten during such a closing stroke.

In a preferred form of our invention, there is associated with the stationary contact of a circuit interrupter an inertia member, or weight, which provides a bouncesuppressing function, by absorbing a portion of the closing energy of the movable contact. The inertia member may loosely be supported on a guide associated with the stationary contact of the circuit interrupter; or the inertia member may move reciprocally within a dashpot, so that some of the energy is gradually absorbed during the return stroke of the inertia member within such dashpot device.

It is a distinct purpose of the present invention to provide a new metnod of eliminating the contact bounce, which is characteristic of vacuum-type circuit interrupters, thus helping to increase contact life by eliminating the erosion due to arcing during the bounce.

Further objects and advantages will readily become apparent upon reading the following specification, taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a vacuum-type circuit interrupter incorporated in a truck-mounted frame, and adaptable for use in metal-clad switchgear, the contacts being illustrated in the closed-circut position;

FIG. 2 is an enlarged view of the circuit interrupter of FIG. 1, the contacts being illustrated in the opencircuit position;

FIGS. 3-5 illustrate the position of the inertia weight relevant to the position of the contacts during the closing operation of the interrupter;

FIGS. '6 and 7 illustrate experimental test results with and without the use of the inertia member of the present invention, illustrating the bouncing conditions, which are present when the inertia member is not utilized; and,

FIG. 8 is a modified type of inertia member which moves within an air dashpot to gradually absorb some of the energy of the moving inertia member.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, and more particularly to FIG. 1 thereof, the reference numeral 1 generally designates a three-phase circuit interrupter of the vacuum-type adaptable for metal-clad switchgear use. It will be observed that the three vacuum interrupting units 2, 3, 4 are vertically mounted having their ends electrically and mechanically connected to the inner ends of pairs of vertically-spaced terminal bushings 6, 7. As shown in FIG. 1, a movable frame 8 is provided having wheels 9 to enable its insertion and withdrawal from a cell or cubicle (not shown), as well known by those skilled in the art of metal-clad switchgear manufacture. Generally, the stationary disconnecting contacts 10, 11 of each vacuuminterrupter element are conductively engaged by mating stationary main contacts (not shown) provided at the inner end of the associated cell, or cubicle of the metalclad switchgear, as well understood by those skilled in the art.

To effect a closing operation of the interrupter 1, an operating mecchnism 12 of any suitable type, such as the solenoid or stored-energy-type of mechanism may be used, enclosed within the grounded framework 8, to effect upward closing movement of the three insulating operating rods 13 associated with the three vacuum interrupter elements 2-4.

During the opening operation, tripping of the mechanism 12 will cause a rapid downward opening movement of the three operating rods 13, first absorbing a part of the energy provided in the contact compression springs 14, and, following the striking of the nuts 15 associated with the operating roads 13, against the upper surfaces 16a of the bifurcated operating levers 16, an impact opening force is provided to break any welds established between the contacts 17, 18, and to provide a rapid downward opening force thereon.

A distinct application of the present invention is to provide a new method of eliminating the contact bounce, or providing a bounce-suppressing means 19, to eliminate the contact bounce, which is characteristic of all highspeed high-velocity circuit interrupters, and is a particularly critical problem in vaccum-type circuit interrupters, to thus help to increase the contact life by eliminating the erosion due to the arcing during the bounce.

As well known by those skilled in the art, contact bounce is due to the returning of some fraction of the kinetic energy of the movable contact 18, which is stored as strain energy in the fixed contact 17 for a short period of time immediately following impact, back to the movable contact 18. The present invention is particularly suited to increase the fraction of the initial kinetic energy, that is dissipated during impact. The basic principle employed is that which is seen when two coins (not shown), laid on a flat surface, so that their edges are touching, are struck along their line of centers by a third coin. When the moving coin strikes the other two, its kinetic energy is transferred through the second coin, imparting the end coin with that same kinetic energy. The moving coin does not bounce off the middle one, and the middle coin does not move. Thus, the end coin which goes moving off has effectively absorbed all the impact energy of the two A way of incorporating this general principle for use in a circuit interrupter 1, particularly one of the vacuumtype, is illustrated in FIG. 2 of the drawings, wherein it will be observed that the moving contact 18 moves upwardly by the upward motion of the insulating operating rod 13 to strike the stationary contact 17. The movable contact 18, in striking the fixed contact 17, causes a compression wave to pass through the stationary contact 17 to a block of metal 21 having a mass preferably comparable to that of the movable contact 18, plus whatever mass is connected to it. Having been imparted with this kinetic energy, the block of metal 21 moves upwardly on its guide 22. As the block of metal 21 moves upwardly, it prevents a bouncing condition between the separable contacts 17, 18 of the vacuum interrupter 1. In the arrangement illustrated in FIG. 2, the energy member, or energy weight 21 is guided upon a stationary stem 22, which is threaded, as at 23, into the upper end 24a of the stationary rod 24 for the stationary contact 17. As shown, the rod 24, supporting the stationary contact 17, is clamped within a contact block 25, of bifurcated configuration and clamped thereto by bolts 26. This split contact block 25 is, in turn, secured, as by brazing, to a pair of vertically-spaced conducting straps 28, 29, which are secured to the terminal 31 of the stud 32 extending through the upper terminal bushing 6. Similarly, the lower terminal bushing 7 of the device has a terminal end 33, having secured thereto an L-shaped conducting strap 34, which is secured to the lower end 35 of the vacuum interrupter element 4, as shown in FIG. 2. As well known by those skilled in the art, the lower movable contact 18 of the vacuum-interrupting element 4 is secured to a suitable flexible bellows (not shown) to provide an evacuated enclosure 36; and the movable stem 37, supporting the movable contact 18, is secured by a pivotal connection 39 to the actuating lever 16, the latter being stationarily supported upon a fixed pivot pin 40. The outer end of the forked actuating lever 16 has an aperture 161) therethrough, which accommodates the upper stem end 13a of the insulating operating rod 13, the contact-compression spring 14 being interposed therebetween.

During the closing operation, the operating rod 13 moves upwardly causing the bifurcated actuating lever 16 to move in a clockwise direction about its stationary pivot 40. This will effect upward closing movement of the movable contact 18 striking the stationary contact 17 and causing a portion of the closing energy to be transmitted, by the compression wave, to the loose inertia member or weight 21. This will cause the inertia member or weight 21 to move upwardly away from the split contact block 25, thereby absorbing a portion of the closing energy of the movable contact 18. A non-bouncing condition between the separable contacts 17, 18 will thus ensue.

FIGS. 3-5 illustrate the relationship between the separable contacts 17, 18 and the position of the inertia member or weight 21. FIG. 3 shows the contact members in the open position. FIG. 4 shows the contact members 17, 1 8 immediately upon the first contact engagement, wherein the loose inertia member 21 has moved upwardly, and FIG. 5 illustrates the separable contact members 17, 18 during a subsequent time, when the loose inertia member or weight has returned to its stationary condition, and the contacts are fully closed.

FIGS. 6 and 7 illustrate test results, which were achieved in the laboratory by using different weights of inertia members. FIG. 6 shows a bouncing condition, which occurs without the use of the energy or inertia weight of the present invention; and FIG. 7 shows the considerably improved results by utilizing an inertia member 21. A number of tests were made using vacuumtype circuit interrupters, and also using a number of different weights. The results were quite positive. The duration of bounce was decreased with increasing weights, and in particular a weight of 13 pounds caused the bouncing condition to disappear entirely. Tests were also made with a bounc-eliminating weight solidly attached to the vacuum-interrupter unit mounting, to check out the possibility of bounce reduction by increasing the stationary mass. However, the results of these tests were negative, and the bounce duration in fact increased. It was concluded on the basis of the tests that the principles involved in the' present invention have been proven, and eliminate any bouncing condition, which may be present.

FIG. 8 illustrates a modified type of construction 42 in which the inertia member, or weight 21 is confined to a dashpot 44. Preferably a suitable gas, such as air, is provided in the dashpot housing 44a, so that there will be a certain absorption of the energy by the movement of the inertia member 21. In more detail, when the moving contact member 18 strikes the fixed contact .17, the kinetic energy of the moving contact 18 is transferred upon impact to a compression wave through the stationary contact 17 to the block of metal 21. The blockof metal 21 moves upwardly within its sealed housing 4a, which acts as a dashpot. As the metal block 21 moves upwardly, it compresses the air in the housing 44a, which fiows through the annular gap 45 between the metal block 21 and the housing 440, thus dissipating the kinetic energy. Finally, the block of metal 21 stops its upward motion, and begins to fall, compressing the fluid 47 underneath it and rarefying the fluid above it. The fluid 47 is allowed to fiow through the clearance gap 45 between the metal block 21 and the housing 44a, so that the block 21 settles slowly upon the fixed contact support 25, imparting the fixed contact 17 with a minimum of energy, so that no bounce occurs.

The particular construction of the vacuum-type circuit interrupter, set forth in FIGS. 1 and 2, is set forth in detail and claimed in United States patent application filed Feb. 28, 1968, Ser. No. 709,013, by Russell E. Frink, and assigned to the assignee of the instant application.

From the foregoing description of two embodiments of the present invention, it will be apparent that we have provided an improved bounce-suppressing means 19, 42 involving the use of an inertia member, or weight 21 to absorb some of the closing energy of the movable contact 18. It will be apparent that in addition to reducing contact bounce, the present invention has the distinct fadvantage of substantially reducing the shock transmitted to the terminal bushings 6. 7 through the conducting arms 28, 29, 34, and thus effectively eliminating breakage of the porcelain, or ceramic bushings 6, 7 or loosening the copper conductors 32 in the bushings. Another important feature to be noted is that the top of the housing 440 (FIG. 8) need only be two or three inches above the top of the stationary contact 25.

The particular arrangements, described above, are for the purpose of illustration and many modifications of the principle involved are possible. The particular invention has been disclostd as providing a means for eliminating bounce in a vacuum-type circuit interrupter, so to increase the fraction of the impact energy dissipated for the purpose of reducing or eliminating contact bounce. It is, however, to be clearly understood that the principles set forth herein are applicable to other types of circuit interrupters, and are not necessarily confined to vacuum-type interrupters 1.

Although there has been illustrated and described specific structures, it is to be clearly understood that the same were merely for the purpose of illustration, and that changes and modifications may readily be made therein by those skilled in the art without departing from the spirit and scope of the invention.

We claim as our invention:

1. A circuit interrupter comprising, in combination:

(a) a stationary contact;

(b) a movable contact adaptable to strike the stationary contact with substantial energy during the closing operation; and,

(c) an inertia weight associated with the stationary contact capable of independent motion relative to the stationary contact, whereby the inertia weight will absorb a portion of the closing energy of the movable contact during the closing operation of the interrupter.

2. The circuit interrupter of claim 1, wherein the inertia weight is a loose block of metal and rests upon the stationary contact.

3. The combination of claim 2, wherein a guide secured to the stationary contact guides the movement of the loose inertia block.

4. The combination of claim 1, wherein a dashpot confines the movement of the inertia weight.

5. A vacuum-type circuit interrupter comprising, in combination:

(a) means defining an evacuated enclosure;

(b) a stationary contact and a movable contact separable within the evacuated enclosure;

(c) a loose inertia member; and,

(d) said loose inertia member resting independently upon the mounting support of the stationary contact.

6. The combination of claim 5, wherein the loose inertia member is a metallic ring guided upon a fixed guide stem.

7. The combination of claim 5, wherein a dashpot is provided to damp the motion of the loose inertia member.

8. The combination of claim 5, wherein a pivoted operating lever is mechanically connected to the movable contact, and an operating rod having a compression spring at the end thereof compresses the spring against the pivoted operating lever to obtain contact pressure in the closed position.

9. The combination according to claim 8, wherein a lost-motion means is provided between the operating rod and the free end of the pivot operating lever.

10. The combination of claim 8, wherein the compression spring is precompressed.

11. The combination of claim 1, wherein the inertia Weight is roughly equal to the weight of the movable contact and parts associated therewith not considering lost-motion.

References Cited UNITED STATES PATENTS 2,039,630 5/1936 Burwell. 2,492,009 12/ 1949 Sandin et al. 2,532,468 12/1950 Sweger. 2,735,896 2/1956 Olsson 200 HERMAN O. JONES, Primary Examiner 

